March 10, 2022

Silicon Graphics Multibus "IP2" board -- UART

The IP2 has 4 serial ports, all available on the not so convenient 60 pin J1 connector. These are provided by a pair of "DUART" devices (SCN68681). Note that the SCC68681 is a CMOS version of the same thing, so the datasheet or manual for it will suffice.

As a bonus, it includes a 16 bit counter/timer.

There are 16 registers, as follows: 

0 - mode A
1 - status A (w=clock select)
2 - BRG test (w=command A)
3 - Rx/Tx holding register A
4 - port change (w=aux ctrl)
5 - interrupt
6 - CT
7 - CT
8 - mode B
9 - status B (w=clock select)
a - test (w=command B)
b - Rx/Tx holding register B
c - vector
d - ports
e - CT
f - CT
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Tom's Computer Info / tom@mmto.org